JP2795557B2 - Composite roll - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a roll used as a work roll used in hot rolling, and more particularly to a composite roll having a two-layer structure of an inner layer and an outer layer formed by centrifugal casting.

[0002]

2. Description of the Related Art Generally, rolls used for hot rolling of steel materials are required to have various properties such as wear resistance, seizure resistance, heat crack resistance and toughness. Since there is a limit in realizing a single material, a so-called composite roll in which a roll surface is composed of two layers of an inner layer and an outer layer made of different materials is often used.

[0003] That is, while the outer layer material is made of an alloy cast iron such as a high alloy gray cast iron or an alloy ductile cast iron having excellent wear resistance, seizure resistance and heat crack resistance, the inner layer material is made of a tough graphite steel (specially. A centrifugal casting method using high carbon cast iron or spheroidal graphite cast iron (see Japanese Patent Publication No. 60-18484) such as Kaimai 58-90363) or adamite steel (see Japanese Patent Application Laid-Open No. 55-153659). Usually, the inner layer and the outer layer are welded and integrated to form a composite roll.

[0004]

However, in the centrifugal casting method, the outer layer material is cast first, and then the inner layer material is cast.
During casting of the inner layer, the outer layer alloy cast iron is redissolved and mixed into the inner layer material, inevitably lowering the strength of the inner layer, and after casting the roll, especially in the cooling process of heat treatment, or during use as a rolling roll, It had developed into a problem of cracking.

For example, when the inner layer material is graphite steel or adamite steel, the outer layer high alloy cast iron is a high C material containing about 3% by weight of carbon. When the C content becomes extremely high, the inner layer has a structure in which flake graphite is crystallized, and strength and toughness are reduced. When the inner layer material is made of spheroidal graphite cast iron, a flaky graphite cast iron layer generated due to poor spheroidization of graphite at the boundary between the inner layer and the outer layer, or a structure including a chill layer in which a large amount of cementite is precipitated, In addition, strength and toughness decrease. Further, spheroidal graphite cast iron has a lower strength than graphite steel and adamite steel, and therefore is not suitable for recent rolls that require strict strength requirements.

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to solve the above problem advantageously, and to provide a composite roll having a high-strength inner layer without crystallization of flake graphite.

[0007]

Means for Solving the Problems The present inventors diligently studied an inner layer material which does not cause crystallization of flaky graphite even when an outer layer material is mixed in the inner layer and the C content of the inner layer increases, and The present inventors have newly found that the inclusion of Bi and REM in the material suppresses the crystallization of flaky graphite and crystallizes spheroidal graphite, which is advantageous for high strength, and has completed the present invention.

That is, the present invention provides an inner layer which is a trunk shaft portion.
And a composite roll having a two-layer structure of an outer layer welded to the outer periphery thereof, wherein the outer layer is formed of an alloy cast iron material, and the inner layer is formed by :
C: 1.4 to 2.5 wt%, Si: 1.5 to 3.0 wt%, Mn: 0.3 to
1.0 wt%, Ni: 1.5 wt% or less, Cr: 0.8 wt% or less, Mo:
0.5 wt% or less, Bi: 0.0006 to 0.005 wt%, REM: 0.005
A composite roll containing 0.00.02 wt% and S: 0.015 wt% or less, and made of a material consisting of the balance of iron and unavoidable impurities. Further, the inner layer may have a structure containing spherical graphite in an area ratio of 1 to 4%,
Advantageously adapted for implementation.

[0009]

Next, the cylinder in the composite roll according to the present invention will be described.
The reason for specifying the material of the inner layer that is the shaft will be described. C: 1.4 to 2.5 wt% (hereinafter simply referred to as%) If the content of C is less than 1.4%, the melting point of the inner layer material increases and the fluidity decreases, and it is difficult to integrate the inner layer and the outer layer by welding. become. To prevent this, high-temperature casting is required, but high-temperature casting increases the amount of re-melting of the outer layer, making it impossible to secure the required thickness of the outer layer, and increasing the frequency of shrinkage cavities and increasing the roll quality. Therefore, it is difficult to apply high-temperature casting. Therefore, the lower limit of the C content is set to 1.4%. On the other hand, if the content exceeds 2.5%, it becomes difficult to form spheroidal graphite, and flaky graphite is crystallized in a large amount to decrease the strength.
The upper limit was 2.5%.

Si: 1.5 to 3.0%, Si has an effect of suppressing the formation of carbides. If its content is less than 1.4%, it becomes difficult to form graphite, and a large amount of carbides is formed, resulting in embrittlement. Is promoted, but if the content exceeds 3.0%, the effect of suppressing the formation of carbides saturates and the base structure becomes brittle, so that the range is 1.5 to 3.0%.

Mn: 0.3 to 1.0% Mn is a component useful for binding to S and eliminating the adverse effect of S. However, if it is less than 0.3%, its effect cannot be obtained, while on the other hand, it exceeds 1.0%. Even if it is contained, the effect is saturated and carbides are easily formed, which leads to a decrease in strength and toughness. Therefore, the content is set in the range of 0.3 to 1.0%.

Bi: 0.0006 to 0.005%, Bi is the most important component in the present invention, which is indispensable for the formation of spheroidal graphite. The effect is poor if not more than 0.0006%. Since the formation of graphite becomes difficult, the range is 0.0006 to 0.005%.

REM: 0.005 to 0.02%, REM is a component that promotes the formation of good spheroidal graphite by being contained in combination with Bi. The content of REM is required to be 0.005% or more, but exceeds 0.02%. The content is 0.005 to 0.02% because the strength and toughness are reduced by causing the formation of carbides.
Range.

S: 0.015% or less S is a component that inhibits the spheroidization of graphite, and it is preferable to suppress the content to 0.010% or less. Particularly, if the content exceeds 0.015%, the effect becomes remarkable. Therefore, the upper limit is 0.015%. And

Although Ni, Mo and Cr have the effect of strengthening the matrix and increasing the toughness, they are components that do not need to be positively contained, but are inevitably incorporated from the alloy cast iron of the outer layer. Since a large amount of carbides are formed and the strength and toughness decrease, Ni: 1.5%, Cr: 0.8% and
Mo: Suppressed at the upper limit of 0.5%.

Further, the inner layer is made of spherical graphite in an area ratio of 1 to 4
%. This is because if the area ratio is less than 1%, embrittlement and strength decrease occur, while if it exceeds 4%, the amount of graphite becomes excessive and the strength decreases. When flaky graphite is crystallized, the flakes form notches, leading to a decrease in toughness.

Further, it is integrally welded to the outer peripheral portion of the trunk shaft portion.
For the outer layer that forms the outer shell, alloy cast iron suitable for hot rolling is used.
Cr cast iron or the like is suitable, but not limited thereto.

In the production of the composite roll according to the present invention, a molten alloy of cast iron as an outer layer is poured into a rotary mold in an amount equivalent to a predetermined thickness, and then a molten metal as an inner layer is poured to form a roll shaft. Centrifugal casting is particularly advantageously adapted.

[0019]

(Example 1) By centrifugal casting, the outer layer of the roll body was made of an alloy glen cast iron having the composition shown in Table 1, while the inner layer was made of various high carbon cast steels having the composition shown in Table 2. A composite roll having an outer diameter of 1500 mm, an inner diameter of 850 mm and a shaft length of 800 mm was cast. The composite roll thus obtained is
After the strain relief annealing (SR) treatment at 450 ° C., the metal structure and tensile strength of the inner layer were examined. The observation and the results of the investigation are shown in FIGS. 1 to 7 and Table 2.

[0020]

[0021]

[Table 2]

As shown in FIGS. 1 to 4, the inner layers No. 1 to No. 4 of the composition according to the present invention have spherical graphite. Table 2 also shows that the strength is significantly improved. On the other hand, as shown in FIG. 5 and FIG. 7, the inner layers Nos. 5 and 7 having compositions outside the scope of the present invention are shown.
Shows that flake graphite is crystallized and that the strength is significantly reduced from Table 2. Further, since inner layer No. 6 contains a large amount of Cr, carbides are crystallized in a large amount and the strength is reduced. .

(Example 2) By a centrifugal casting method, an alloy ductile cast iron having a composition shown in Table 3 was used for an outer layer of a roll drum, and various high carbon cast steels having a composition shown in Table 4 were used for an inner layer. , Outer diameter: 1500mm, inner diameter: 850mm and shaft length: 800mm
Was cast. The composite roll thus obtained was subjected to a high-temperature heat treatment (quenching after heating at 950 ° C. for 10 hours) and a tempering heat treatment (holding at 550 ° C. for 25 hours), and the metal structure and tensile strength of the inner layer were examined. The results of the observations and investigations are shown in FIGS.

[0024]

[0025]

[Table 4]

As shown in FIG. 8, the inner layer No. 8 having the composition according to the present invention has spherical graphite formed therein, and Table 4 shows that the strength is remarkably improved. In the inner layer No. 9 having a metallographic structure shown in FIG. 9 and having a composition outside the range of the present invention, flake graphite is crystallized, and Table 4 shows that the strength is significantly reduced.

[0027]

According to the present invention, since the strength of the inner layer of the composite roll is improved, accidents such as roll cracking during rolling can be prevented, and the tolerance of the tensile stress applied to the inner layer during roll production or heat treatment. Therefore, low-temperature quenching for the purpose of increasing the strength and toughness of the outer layer and increasing the cooling rate during quenching are possible. Further, since the composite roll of the present invention can be easily manufactured by the same method and equipment as the conventional manufacturing of this type of composite roll, there is also an advantage of reducing the manufacturing cost.

[Brief description of the drawings]

FIG. 1 is a photograph of a metal structure of an inner layer.

FIG. 2 is a photograph of a metal structure of an inner layer.

FIG. 3 is a photograph of a metal structure of an inner layer.

FIG. 4 is a photograph of a metal structure of an inner layer.

FIG. 5 is a photograph of the metal structure of the inner layer.

FIG. 6 is a photograph of a metal structure of an inner layer.

FIG. 7 is a photograph of the metal structure of the inner layer.

FIG. 8 is a photograph of a metal structure of an inner layer.

FIG. 9 is a photograph of the metal structure of the inner layer.

Claims (2)

(57) [Claims] 1. An inner layer which is a body shaft portion and welded to an outer periphery thereof.
And the composite roll consisting of 2-layer structure of an outer layer, the outer layer is formed of an alloy cast iron, the inner layer, C: 1.4 ~2.5 wt%, Si: 1.5 ~3.0 wt%, Mn: 0.3 ~1.0 wt%, Ni : 1.5 wt% or less, Cr: 0.8 wt% or less, Mo: 0.5 wt% or less, Bi: 0.0006 to 0.005 wt%, REM: 0.005 to 0.02 wt% and S: 0.015 wt% or less, with the balance iron and unavoidable A composite roll formed of a material comprising: Wherein the inner layer, the composite low <br/> le according to claim 1 having a structure containing at 1-4% range spheroidal graphite area ratio.